Influence of Particle Size of Fly Ash on Compressive Strength of Concrete

อิทธิพลจากขนาดอนุภาคของเถ้าถ่านหินที่มีต่อกำลังอัดของคอนกรีต

Name: Songpiriyakij, Smith

Organization : มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี

keyword: Concrete

; Fly ash

; Packing Effect

; Pozzolanic Reaction

; Model

Abstract: The objectives of this research are to investigate the packing behavior of fly ash particles in mortar and concrete and to establish a model to predict the compressive strength of fly ash concrete. The amount of fly ash used in the mix and its fineness arethe two major variables considered in the model. The study shows that the model is ableto predict the short and long-term compressive strength of fly ash mortar (a mixture with the flow of 110_+5) and concrete from 25-30 MPa at the curing ages ranging from 3-180 days.The mix proportions of concrete used in this study are designed in accordance with the methods suggested by the American Concrete Institute (ACI). Part of Portland cement Type I in the mixes is replaced with the Mae Moh fly ash and ground river sand, of which eachhas four different sizes. The selected water to cementitions materials ratios are used asanother controlled parameter.The results showed that when 20 percent of cement in these mortar mixes was replaced byfly ash, regardless of its size (fine or coarse), there was no apparent strength contribution due to pozzolanic reaction during the first two weeks. When the cementreplacement by fine fly ash increased to 40 percent, the pozzolanic reaction was observedwithin 7 days, and shorten to 3 days for 60 percent cement replacement. This implies thatthe rate of pozzolanic reaction depends on both the fineness and the amount of fly ash replecement. During the period of no pozzolanic reaction, fly ash, as any fine particle, fills the voids between cement grains densifying the matrix, a phenomenon commonly knownas "packing" effect. In this study, test shows that fly ash, at early age and with no pozzolanic reaction, contributes to the compressive strength of cementitious matrices inthe same way as non-reactive ground river sand.A linear relationship was observed between the normalized compressive strength (NCS) of concrete and the mean diameter (d50) of ground river sand when used as cement replacementof 20-60 percent. When using fly ash of the same replacement ratio in the concrete mixes, the same relationship was found to be a logarithmic function. There was no conclusive evidence that the water to binder ratio had any influence on the pozzolanic reaction during the first 3 days. However, this effect becomes more visibly recognized after 7 days and as the water to binder ratio gets lower, the faster this rate becomes. This leads to the conclusion that the pozzolanic reaction also depends on the fineness and the amount of fly ash replacement and the water to binder ratio. For coarse fly ash, there was no indication that it enhances concrete properties better than coarse ground river sand. Lastly, the results predicted by the proposed model were in good agreement with experimentdata as well as with those previously reported by other investigations.

มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี

Address: กรุงเทพมหานคร (Bangkok)

Email: info.lib@mail.kmutt.ac.th

Name: Assoc.Prof. Chai Jaturapitakkul

Role: Supervisor

Created: 2545

Issued: 2006-03-08

Modified: 2006-05-10

วิทยานิพนธ์/Thesis

ISBN: 9744564431

CallNumber: CVE1934

tha

DegreeName: Doctor of Philosophy

Level: Doctoral Degree

Descipline: Civil Engineering

Grantor: King Mongkut's University of Technology Thonburi

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